Enhanced etching/smoothing of dielectric surfaces

ABSTRACT

A gas cluster ion beam (GCIB) etching apparatus having a system for producing a gas cluster ion beam utilized to controllably etch a substrate. The gas cluster ion beam is initially directed along a preselected longitudinal axis. A portion of the GCIB etching apparatus is operably connected to the beam producing system and contains the substrate to be etched when impacted by said gas cluster ion beam. The portion of the GCIB etching apparatus includes a system for directing the gas cluster ion beam in a direction offset from the preselected longitudinal axis while permitting unwanted ionizing radiation to remain directed along the longitudinal axis. A substrtate holder is located within a portion of the GCIB etching apparatus for positioning the substrate in line with the offset gas cluster ion beam during the etching process, and the unwanted ionizing radiation being substantially prevented from impinging upon the substrate during the etching process.

BACKGROUND OF THE INVENTION

This invention relates generally to the smoothing of dielectricsurfaces, and, more particularly to the etching/smoothing of dielectricsurfaces wherein it is desirable to avoid exposing such dielectric tothe effects of ultraviolet radiation, X-ray radiation and/or ionizingelectromagnetic radiation.

As integrated circuit device sizes have been shrunk to create denser,more functional devices, the gate delays of the devices have typicallybecome shorter and the devices have become faster. However, thecorresponding shrinking of the integrated circuits' interconnectingmetal lines and of the inter-metal dielectric insulators, has resultedin increased signal propagation delays. These increasing interconnectionpropagation delays have generally resulted from the increased resistanceof the thinner metal interconnect lines and the increased capacitancethat results from closer spacing of conductors and from the thinnerinsulating dielectric layers which are necessitated. This situation,which is well known in the integrated circuit development community,poses a barrier to continued successful increases in integrated circuitdensity, speed, and functionality.

In order to continue shrinking integrated circuit devices whilemaintaining or improving their speeds, designers of integrated circuitinterconnect are finding it necessary to reduce the resistivity of themetals used and to reduce the inter-metal (both interline andinterlayer) capacitances. This trend can be noted in the developingshift from the longstanding use of aluminum interconnect metal to theuse of lower resistivity copper. It can also be noted in the developingshift from the use of SiO₂ as the dielectric material of choice (havingdielectric constant, k≅3.9) towards the use of dielectric materialshaving a lower dielectric constants (low-k materials) in the range of3>k>1. In order for future generations of integrated circuits to meettheir performance goals, the materials and methods for routinefabrication of low-k materials for inter-metal dielectric insulationmust be developed. One example of an interconnecting structure which isbeing developed to take advantage of lower resistivity metal conductorsand low-k inter-metal dielectric materials is known in the semiconductorindustry as “copper dual damascene interconnect.”

Because of the critical nature of this problem for the integratedcircuit manufacturing community, a very large effort is being expendedto identify and develop low-k materials and methods for theirincorporation into the product process flow. In addition to lowdielectric constant, there are many other requirements for suitableinsulating materials. These include low cost, high leakage resistance,mechanical strength, thermal stability, non-corrosiveness, compatiblecoefficient of expansion, ease of deposition, gap filling ability,appropriate etching characteristics, ability to act as a migrationbarrier, and numerous other desired characteristics. No material appearsto satisfy all requirements, and so the industry is examining tradeoffsbetween various possible materials.

One class of low-k materials that is of considerable interest is afamily of fluorine-containing polymers generally known as parylenes.These materials have been successfully applied for some time in avariety of industries where conformal dielectric coating of complexshapes has been required. At least two parylenes known as parylene-N andparylene-F have been discussed by R. S. List, et. al. in MRS Bulletin,October, 1997, p.61. They show that these parylenes have properties thatare considered favorable for use as potential low-k (k<2.5) integratedcircuit dielectric materials and methods have been devised (for examplethose taught in U.S. Pat. No. 5,879,808—Wray, et. al.) for fabricatingthem into the multi-level structures required separating circuitinterconnection layers.

Historically, SiO₂ has been used as the primary dielectric material forsilicon integrated circuits. A factor in it's longstanding utility hasbeen the ease and precision with which it can be etched into a desiredpatterns and thickness using wet chemistry etchants such as hydrofluoricacid and the like. As device geometries have become smaller, there hasbeen an increase in the use of dry etching techniques because of theirtendency to be able to produce finer patterns. Most modern low-kdielectric materials including parylene have been generally understoodto be best etched using dry etching methods such as plasma etching, ionetching, and the like, rather than by wet etching.

A problem exists, however, in that plasma etching and other dry etchingprocesses are known to sometimes leave a degree of damage on and beneaththe etched surfaces. Furthermore, conventional dry etching processes(plasma etching, reactive ion etching, conventional ion etching, sputteretching, and ion beam milling) all unavoidably expose the etched surfaceto electromagnetic radiation including ultraviolet wavelengths—becausethe substrate to be etched is directly exposed to radiation from theassociated plasma.

Fluorine-containing polymers (fluoropolymers) such as parylene canreact, upon exposure to ultraviolet of appropriate wavelengths, toliberate fluorine, which though chemically unbound may remain entrappedin the fluoropolymer matrix. Adjacent metal interconnect layers mayeventually react with the corrosive free fluorine, resulting in ashortened useful lifetime of the integrated circuit. This creates apotential integrated circuit device reliability problem.

There is a need for a dry etching technique capable of efficientlyproducing uniformly homogeneous etching over large diameter (200-300 mmor larger) wafers without residual damage and without producing residualfree fluorine in order to enable greater success in the application offluoropolymers (such as parylenes) for use as inter-metal low-kdielectrics in future integrated circuit generations.

The concept of using gas cluster ion beams (GCIB) for dry etching,cleaning, and smoothing of hard materials is known in the art and hasbeen described by Deguchi, et.al in U.S. Pat. No. 5,814,194. Becauseionized clusters containing on the order of thousands of gas atoms ormolecules may be formed and accelerated to modest energies on the orderof a few thousands of electron volts, individual atoms or molecules inthe clusters each only have an average energy on the order of a fewelectron volts. It is known from the teachings of Yamada, U.S. Pat. No.5,459,326, that such individual atoms are not individually energeticenough to significantly penetrate a surface to cause the residualsurface damage typically associated with the other types of dry etchingin which individual atoms have energies on the order of hundreds orthousands of electron volts. Nevertheless, the clusters themselves aresufficiently energetic (some thousands of electron volts) to effectivelyetch, smooth, or clean hard surfaces.

An important consideration in the ion beam processing of surfacescovered by insulating films (as is the case when fluoropolymer films aredeposited on semiconductor wafers) is the tendency for the charged beamto induce charging of the surface being processed (etched, in thiscase). If sufficient charge is permitted to accumulate on the insulatingsurface without means for dissipation, the dielectric properties of thefilm may be exceeded and the film can be ruptured or otherwisepermanently damaged by the electrical stress. This problem is well knownin ion beam processing such as ion implantation, ion milling, and GCIBprocessing. It is to be expected that means of limiting the surfacecharging of fluoropolymer films during GCIB etching must be provided ifundesirable and harmful charging is to be avoided. When the positivecluster ions strike the insulating film, they may transfer their chargeto the film. The collision process also results in the liberation ofsecondary particles from the surface—surface atoms thus liberated resultin the etching of the surface. The liberated secondary particles may beelectrons, neutral atoms, or charged atoms. Free electrons are much moremobile than free charged atoms (ions) and are likely to escape. Thus,the main tendency of the release of secondary particles is to increasethe positive charging of the surface. Such charging can produce damageto the insulating material and has prevented the successful priorapplication of ion cluster beam processing to some insulating surfaces.

It is therefore an object of this invention to provide a GCIB systemcapable of efficiently producing uniformly homogeneous etching overlarge diameter (200-300 mm or larger) substrates without residual damageand without producing residual free fluorine in order to enable greatersuccess in the application of fluoropolymers (such as parylenes) for useas inter-metal low-k dielectrics in future integrated circuitgenerations.

It is another object of this invention to provide a GCIB system whichsubstantially eliminates the problems associated with the production ofundesirable ultraviolet and X-ray radiation.

It is a further object of this invention to provide a method forefficiently etching large diameter (200-300 mm or larger) substrateswithout residual damage due to electrical charging or to deep surfacepenetration by light ions and without exposing the substrates toionizing electromagnetic radiation.

It is still another object of this invention to provide a GCIB systemwhich substantially eliminates the electrical charging of an insulatingsurface to be etched.

SUMMARY OF THE INVENTION

The objects set forth above as well as further and other objects andadvantages of the present invention are achieved by the embodiments ofthe invention described hereinbelow.

This invention provides a dry etching gas cluster ion beam (GCIB)apparatus and process for, preferably, etching/smoothing fluoropolymerlayers and thin films. The process of this invention results inproducing a smoother surface, a surface with less subsurface damage, asurface without charging damage to the fluoropolymer, and a surfacewithout free fluorine impurities caused by ultraviolet or X-rayradiation. The invention accomplishes this end by including means withina portion of a GCIB etching apparatus for directing the gas cluster ionbeam in a direction offset from a preselected axis while permittingunwanted ionizing radiation (ultraviolet, X-ray and electromagneticradiation) to remain directed along the preselected axis. The substrateto be etched being positioned in line with the offset gas cluster ionbeam. This invention, therefore, facilitates the successful andefficient application of fluoropolymer and other fluorine bearinginsulating dielectric materials to the problem of low-k dielectricinsulation between conductors in integrated circuit interconnectsystems. For a better understanding of the present invention, togetherwith other and further objects thereof, reference is made to theaccompanying drawings and detailed description and its scope will bepointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art plasma etch or reactive ion etch configuration,showing exposure of the substrate to be etched to ultraviolet radiationgenerated in the plasma;

FIG. 2 is a prior art ion milling configuration, showing exposure of thesubstrate to be etched to ultraviolet radiation generated in the plasmain the ion source;

FIG. 3 represents a prior art gas cluster ion beam processing system;

FIG. 4 represents a gas cluster ion beam processing system of thepresent invention to avoid UV irradiation of the substrate to be etched;

FIG. 5 represents an alternate embodiment of the gas cluster ion beamprocessing system of the present invention to avoid UV irradiation ofthe substrate to be etched;

FIG. 6 represents undesirable charging of a dielectric layer occurringduring gas cluster ion beam processing; and

FIG. 7 represents a further preferred embodiment of the gas cluster ionbeam processing system of this invention for etching insulating surfaceswithout damage due to surface charging.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to better understand the present invention it is desirable todescribe the prior art systems in which the substrate to be etched (alsoreferred to as smoothed) is directly exposed to the radiation from theassociated plasma reference is made to FIGS. 1 and 2 of the drawings.For example, FIG. 1 shows a plasma etch or reactive ion etch system 10in which the substrate to be etched 11 rests on lower electrode 16. Lowpressure gas which may be inert or reactive is introduced through gasport 14. A plasma 12 is generated in the region between upper electrode15 and lower electrode 16. Through action of the plasma 12, thesubstrate 11 is etched or reactively etched. Plasma 12 producesradiation including ultraviolet radiation. There is a directline-of-sight path 13 for the ultraviolet radiation to travel from theplasma 12 to the substrate 11. Although not shown in FIG. 1, plasma etchor reactive ion etch equipment may sometimes use a ultraviolet emittingigniter to trigger plasma formation—in such cases radiation from theigniter may also strike the surface to be etched.

FIG. 2 shows an ion milling system 20 having a Kaufman type or similarion source 22 into which is introduced a low pressure gas through a gasport 23. A plasma 24 is generated within the source 22 and an ions 26are formed into a beam directed from source 22 to substrate 21 foretching substrate 21. The plasma 24 produces radiation includingultraviolet radiation. Because there exists a direct line-of-sight path25 from the plasma 24 to the substrate 21 being etched, ultravioletradiation from the plasma 24 strikes the substrate 21.

FIG. 3 shows a typical configuration for a gas cluster ion beamprocessor 30. The processor is enclosed in a vacuum vessel 33 consistingof a source chamber 43 and a processing chamber 44. Although notrequired, it may sometimes be desirable to also employ a differentialvacuum pumping chamber 42 to help isolate the downstream regions fromthe higher pressure upstream regions. The interior of vacuum vessel 33is maintained at a vacuum reduced pressure by vacuum pumps 34A, 34B,34C, and 34D. A source gas 46 is introduced through gas feed tube 45.Gas clusters 31 are formed by creating a supersonic jet of source gasthrough a properly shaped nozzle 32 into the source chamber 43 which isat a substantially reduced pressure. Cooling resulting from theexpansion causes the gas to condense into clusters of from several toseveral thousand atoms or molecules. A gas skimmer aperture 35 is usedto separate the gas products that have not been converted into a clusterjet from the cluster jet so as to minimize pressure in the downstreamregions where such higher pressures would be detrimental (e.g., ionizer36, accelerator high voltage electrodes 38, and processing chamber 44).Suitable source gases 46 are, for example, argon, other inert gases,oxygen, nitrogen, oxygen bearing gases such as carbon dioxide, andnitrogen bearing gases. Inert gases etch the substrate surfaces bymechanical action. Because, during cluster impact, transiently hightemperatures and pressures obtain, chemical reactions are facilitated.Therefore, reactive gases like oxygen or oxygen bearing gases areadditionally effective because surface chemical reactions can acceleratethe mechanical etching effect. Of course, mixtures of inert gases withreactive gases are also possible. Fluoropolymers are hydrocarbons and sowill be readily oxidized under cluster impact conditions. Nitrogen isalso known to decompose parylene at high temperatures. Oxygen, nitrogen,and oxygen or nitrogen bearing gases are likely to be effective GCIBetchants for fluoropolymers.

After the cluster jet has been formed, the clusters 31 are ionized in anionizer 36. The ionizer 36 is typically an electron impact ionizer thatproduces thermoelectrons from one or more incandescent filaments andaccelerates and directs the electrons causing them to collide with thegas clusters 31 in the gas cluster jet where it passes through theionizer 36. The electron impact ejects electrons from the clusters,causing the clusters to become positively ionized. A set of suitablybiased high voltage lens electrodes 37 extracts the cluster ions fromthe ionizer and focuses them to form a gas cluster ion beam. Another setof high voltage accelerator electrodes 38 accelerates the beam to adesired energy, typically from 1 keV to several tens of keV. Theaccelerated beam is directed at a substrate 41 for GCIB processing. Notshown, but sometimes utilized, is a mass selector for selecting clustersof a certain mass or within a certain range of masses. Such massselector can be, for example, a weak transverse magnetic field fordeflecting monomer ions and other light ions (e.g., those cluster ionsof ten or fewer atoms or molecules) out of the beam and passing moremassive cluster ions.

Since the fluoropolymer etching application contemplates the etching oflarge diameter wafers with spatially uniform results, a scanning system47 is desirable in order to uniformly scan the gas cluster ion beam(GCIB) across large areas to produce spatially homogeneous results. Twopairs of orthogonally oriented electrostatic scan plates 39 and 40 makeup scanning system 47, and having suitable beam scanning voltagewaveforms imposed can be utilized to produce a raster or other scanningpattern across the desired area.

There are three problems that interfere with the straightforwardapplication of GCIB processing as shown in FIG. 3 to the etching offluoropolymers. The first problem results from the possible productionof a small amount of ultraviolet ionizing radiation in the ionizerregion and the potential for that radiation to reach the substrate beingprocessed where it could produce the detrimental effects described inthe discussion of the prior art. The ionizer section, as has beenmentioned, typically contains incandescent filaments and creates aregion populated with accelerated electrons, low energy secondaryelectrons, and positive ions, both monomers and clusters of all sizes.Neutral gas molecules are also present. It is possible that glowdischarges and other plasma effects can take place, potentiallyproducing undesirable ultraviolet (UV) radiation. Furthermore, thefilaments for producing the thermoelectrons produce light including a UVcomponent. In the system shown in FIG. 3, there is line-of-sight fromthe ionizer region to the substrate processing chamber, where thefluoropolymer containing substrate to be etched is disposed. Asdiscussed above, that UV component, even though small, could leave freefluorine in the etched material with the attendant ill effectspreviously described.

The second problem has to do with the production of low energy ionizingX-radiation (X-rays) in the ionizer, lens, and accelerator regions andthe potential for that radiation to reach the substrate being processedwhere it can produce the same detrimental effects ascribed to UVradiation in the discussion of the prior art, namely the formation ofcorrosive free fluorine in the fluoropolymer. X-rays are produced by thebremsstrahlung process when electrons are attracted to and strikepositively charged electrodes. The presence of electrodes charged atpotentials of up to a few tens of kilovolts in the ionizer, lens, andaccelerator regions of the GCIB process machine, and the availability offree electron. Free electrons are generated in the ionizer, in the beamby collision of the beam with residual gas in the vacuum, and bysecondary electron emission from the vacuum enclosure inner walls whenstray ions strike the walls.

The third problem results from the fact that, while etching with GCIB,the bombardment of insulating films such as parylenes by the positivelycharged ions in a GCIB may induce electrical charging of the insulatingsurface being etched. As described hereinbefore, such charging canrupture or otherwise damage the insulating film.

The preferred embodiments of the present invention provide a system andtechnique for substantially eliminating or ameliorating these threeproblems.

One way of eliminating the undesirable effects of UV on fluoropolymersis to eliminate the UV entirely. Since the ionizer is a potential sourceof UV in a GCIB process machine, one could eliminate the source of UV byionizing the beam in a way that did not produce any glow discharge anddid not have an incandescent filament. This could be done by ionizingthe beam using a radioactive beta source as the source of ionizingelectrons.

Alternatively, ionization could be performed by using a laser or otherintense light source to photo-ionize the clusters. By directing thelaser or light source so as to avoid purposeful transmission of any UVtoward the substrate to be etched, the undesirable effects of UV on thesubstrate to be etched due to the light source can be minimized.

A preferred embodiment of the present invention, however, utilizes aconventional electron impact ionizer that may produce a small amount ofUV, but takes advantage of the beam-nature of the GCIB process toeliminate line-of-sight from the potential UV forming region to thesubstrate processing region. This system of eliminating UV from strikingthe substrate being etched is preferred because it has the addedadvantage that it can also prevent X-rays generated in the ionizer,lens, or accelerator regions from reaching the substrate being etched bysimultaneously eliminating line-of-sight from the X-ray forming regionsto the substrate processing region.

FIG. 4 shows one of several possible embodiments of the inventionutilizing of a basic GCIB apparatus configuration that can virtuallycompletely eliminate the possibility of UV or X-rays reaching thesubstrate 41 to be etched. In this embodiment, a fixed (DC) deflectionvoltage has been added to the beam scanning voltage waveforms at theY-scan deflection plates 62 to impose a fixed offset angle 68 betweenthe initial beam path and the path of the scanned GCIB 65, the offsetbeing imposed in the region between the scan plates 62. At scan plates62, in addition to being deflected in the amount of offset angle 68, theGCIB also is scanned through a scanning angle 69. One half of the scanangle 69 is referred to as the scan half angle 70. The UV radiation andX-rays are not responsive to the electrostatic field between scan plates62 and continue in a straight line 63 to an impact point 66 in a regionnow separated from the substrate 41 processing region by the GCIB fixedangular deflection. As shown, collimator 61 and baffle arrangements 64A,64B, 64C, and 64D can be added in combination with the angular beamoffset to further reduce the likelihood of stray reflections directingeven a small amount of UV to the substrate 41 processing area. It isespecially important that the impact point 66 of the undeflected UV andX-ray radiation be baffled from the substrate 41 processing area, and inthe example shown in FIG. 4, baffle 64C serves this purpose. It is alsoimportant that the scanned GCIB 65 enter the baffled region and beenclosed in the baffle and thus separated from the straight line path63. Substrate 41 is held and positioned in the path of the scanned beam65 and away from the path of the undeflected UV and X-ray radiation bysubstrate holder 67. If the baffles 64A, 64B, 64C and 64D and thecollimator 61 are formed of or have a layer of a material which absorbsX-rays, then they are also effective to prevent X-rays from reaching thesubstrate 41. The selection of X-ray absorbing materials (such as heavymetals, e.g., lead) and the determination of the necessary thickness ofsuch material (typically a few millimeters in this case) is well knownto those who practice the art of X-ray shielding.

FIG. 4 further shows, for purposes of example, but not for limitation, afixed angular deflection or offset angle 68 of the GCIB of approximately15 degrees from the initial beam trajectory. However, it is apparentthat any deflection angle larger than the scan half-angle 70 ispotentially adequate to separate the GCIB from the electromagneticradiation beam (UV or X-ray), provided that the undesired UV beam can beadequately collimated. Although we have illustrated the case whereionization is by electron impact, it can be appreciated that method andsystem of this invention can also be used to separate a GICB from strayUV resulting from the use of a photo-ionizing light source.

As shown in FIG. 4, an electrostatic deflection element 62 is used toseparate the GCIB from the potential UV beam. Of course, other schemesfor deflecting the GCIB from the potential UV beam could also be used.For example, a sector magnet could be used to deflect the beam whileallowing the UV and X-rays to pass undeflected. In general we consideran electrostatic form of deflection to be the preferred method forseveral reasons:

1. The GCIB will normally contains cluster ions of a range of masses.Although as mentioned earlier, mass selection filters are known, it isnot general practice to select only cluster ions of one specific mass orof a very narrow range of masses. To do so would result in thediscarding of a large number of cluster ions of the rejected massesresulting in a much lower mass flux, which would result in a reducedetch rate. For this reason, it is advantageous to retain all clusterions of greater than a predetermined mass. The ionizer typicallyproduces or is typically adjusted to produce a preponderance of clusterions that are singly ionized—one electron has been removed. All ions areaccelerated by falling through an electrostatic potential field of apredetermined voltage, typically some few to few tens of kilovolts. Thusthe great majority of gas cluster ions have the same charge (+1) and thesame energy (E=Va, where Va is the acceleration potential), but wherethey have a wide range of velocities due to the fact that they have acontinuous range of masses from several to several thousands of atomicor molecular weights. Thus the great majority of the cluster ions havethe same electrostatic deflection stiffness, but have widely differingmagnetic deflection stiffnesses. A GCIB having a range of cluster sizesresponds uniformly to an electrostatic deflection element, but amagnetic deflection element will also tend to disperse the masses, whichin general is undesirable.

2. Readily controllable electrostatic elements can generally bemanufactured for a lower cost than similarly controllable magneticelements.

3. Power consumption of electrostatic elements is generally lower thanthat of magnetic elements.

4. Electrostatic fields are readily contained by the metal containersusually employed as vacuum vessels, while magnetic fields are moredifficult to shield and when unshielded can introduce workplace hazardsand can interfere with sensitive equipment.

Still referring to FIG. 4, the electrostatic deflection angulardeflection function has been shown combined with an electrostaticscanning function in a pair of electrostatic scanning/deflecting plates62, which replace the simple scanning-only electrostatic scanning plates39 used in the prior art shown in FIG. 3. This is convenient andefficient. However it is readily appreciated that such configuration isnot the only one that can be effective and that there are alternateembodiments of this invention. For example, an alternate embodiment isshown in FIG. 5 which uses an “electrostatic mirror” element 74 tointroduce a 90 degree deflection from the initial trajectory of theGCIB, while permitting any potential UV beam 63 to travel undeflected.

The electrostatic mirror element 74 is a plate and grid arranged andelectrically biased so as to reflect the GCIB at an approximately 90degree angle from the path of the beam 63 of ultraviolet or X-rayelectromagnetic radiation. The plate has a hole 76 to permit passage ofany UV or X-ray beam 63 that may be present. The mirror power supply 75applies a retarding potential greater than Va, the beam accelerationpotential. The grid and the negative side of the mirror power supply aregrounded to the wall of the vacuum vessel 33. A potential advantage ofthis arrangement is that it shortens the overall length of theapparatus. A potential disadvantage is that the grid of the mirror 74 isstruck by the GCIB and could experience sputter erosion. It can beappreciated that alternative means of deflecting and baffling so as toseparate the GCIB from the possible UV beam and to remove the substrateto be etched from the influence of the UV may also be used within thespirit of the present invention.

FIG. 6 schematically illustrates a stage in processing of asemiconductor substrate 41. A fluorocarbon dielectric layer 97 on top ofpreviously processed conductive layer 98 is being smoothed by GCIBprocessing. The substrate 41 is disposed on a substrate holder 67 thatis grounded and, which mechanically supports the substrate 41 duringprocessing. The substrate 41 is grounded by the holder 67. Charge fromthe bombarding scanned GCIB 65 is transferred to surface of thefluorocarbon dielectric layer 97. Electrons tend to flow from groundthrough the substrate holder 67, the substrate 41, and the conductivelayer 98 on the substrate 41 in order to neutralize the positive chargesarriving with the gas cluster ions 96 in the scanned GCIB 65. Thisinduces electrical stress in the fluorocarbon dielectric layer 97.Charge building across the dielectric 97 can stress it and may rupturethe dielectric layer and discharge. To be certain of high yieldproduction of semiconductor devices, it is necessary to avoid thedielectric-stressing and electrical discharge problem illustrated inFIG. 6. In order to eliminate the problem of electrical charging of thelow-k dielectric films during processing with the positive ion clusterbeam, it is necessary to make available a source of available electronsto the dielectric surface so that they may continuously neutralize thesurface to prevent accumulation of a harmful charge across thedielectric layer 97.

This may be accomplished in any of several ways. A source ofthermoelectrons (e.g. a hot filament) may be placed in the vicinity ofthe substrate to be etched. A source of low energy secondary electronsgenerated from collision of an accelerated beam of electrons with asurface in the vicinity of the substrate to be etched may be used. Aplasma bridge source of low energy electrons may be conveyed to thesubstrate to be etched by a neutral plasma in the substrate processingarea. All of these methods are viable methods of neutralizing anypositive charge that would otherwise tend to accumulate on the surfaceof a fluoropolymer dielectric film being etched by a GCIB method.Without such measures, damage from charging is likely to result in suchnegative consequences that the otherwise useful and novel process mightbe severely impaired in usefulness. FIG. 7 shows further embodiment ofthe GCIB system of this invention similar to that shown in FIG. 4 for UVfree etching of fluoropolymer dielectric layers including modificationsto minimize the effects of surface charging due to the use of positivecluster ions as the etching means. The substrate processing region issurrounded with a Faraday enclosure 81 having a suppressor ringelectrode 87 at the beam entrance opening of the Faraday enclosure 81.The suppressor ring electrode 87 is negatively biased with respect tothe Faraday enclosure 81 by suppressor power supply 82 so as to permitentrance of the cluster ions 65 with minimal influence, but yet alsoprevent the exit of electrons, retaining all secondary electrons in theFaraday enclosure where they may be returned to the substrate 41.Additionally, an active electron gun 85 powered by filament power supply83 and anode power supply 84 is attached to the side-wall of the Faradayenclosure 81. The gun 85 is configured and biased to project a beam ofprimary electrons 88 to the opposite wall of the Faraday enclosure 81.The primary electron beam 88 induces the emission of low energysecondary electrons 89 from the Faraday enclosure wall. These low energyelectrons 89 may flow to the substrate 41 as required to minimizepositive charging due to arrival of the positive cluster ions 65. Insome cases it may be desirable to control the amount of etching thatoccurs by measuring the total amount of positive gas cluster ions thatstrike the substrate 41. In such a case, a lead 86 from the Faradayenclosure 81 conducts charge to an integrator 90 that integrates thecharge to provide an indication of etch process progress.

Although the invention has been described with respect to variousembodiments, it should be realized this invention is also capable of awide variety of further and other embodiments within the spirit andscope of the appended claims.

What is claimed is:
 1. A gas cluster ion beam (GCIB) etching apparatus comprising: a system for producing a gas cluster ion beam utilized to controllably etch a substrate, said gas cluster ion beam initially being directed along a longitudinal axis; a portion of the GCIB etching apparatus being operably connected to said beam producing system, said portion containing the substrate to be etched when the substrate is impacted by said gas cluster ion beam; said portion of the GCIB etching apparatus including means for directing said gas cluster ion beam in a direction offset from said longitudinal axis while permitting unwanted ionizing radiation to remain directed along said longitudinal axis; and means within said portion of the GCIB etching apparatus for positioning the substrate in line with said offset gas cluster ion beam; wherein said unwanted ionizing radiation is substantially prevented from impinging upon the substrate during the etching process.
 2. A GCIB etching apparatus as defined in claim 1 wherein said unwanted ionizing radiation contains UV radiation.
 3. A GCIB etching apparatus as defined in claim 1 wherein said unwanted ionizing radiation contains X-ray radiation.
 4. A GCIB etching apparatus as defined in claim 1 wherein said unwanted ionizing radiation contains both UV and X-ray radiation.
 5. A GCIB etching apparatus as defined in claim 1 wherein said unwanted ionizing radiation is electromagnetic radiation.
 6. A GCIB etching apparatus as defined in claim 1 wherein said means for directing said gas cluster ion beam comprises means for providing an electrostatic field which deflects said gas cluster ion beam toward the substrate.
 7. A GCIB etching apparatus as defined in claim 6 further comprising a baffle at least partially encompassing the substrate.
 8. A GCIB etching apparatus as defined in claim 7 wherein said baffle includes an entrance portion for permitting said offset gas cluster ion beam to pass onto the substrate.
 9. A GCIB etching apparatus as defined in claim 7 further comprises a collimator in combination with an additional baffle for assisting in the prevention of said unwanted ionizing radiation from reaching the substrate.
 10. A GCIB etching apparatus as defined in claim 8 wherein said baffle comprises material which is capable of absorbing X-ray radiation.
 11. A GCIB etching apparatus as defined in claim 8 wherein said collimator comprises an aperture located within said additional baffle.
 12. A GCIB etching apparatus as defined in claim 1 further comprising a scanning system which is capable of scanning said beam of ionized electromagnetic radiation through a scan angle and wherein said offset gas cluster ion beam is offset at an angle larger than half said scan angle.
 13. A GCIB etching apparatus as defined in claim 1 wherein said offset gas cluster ion beam is offset from said longitudinal axis at an angle of approximately 15 degrees.
 14. A GCIB etching apparatus as defined in claim 1 wherein said means for directing said gas cluster ion beam comprises a reflective element assembly which deflects said gas cluster ion beam toward the substrate.
 15. A GCIB etching apparatus as defined in claim 14 wherein said reflective element assembly comprises an electrostatic mirror.
 16. A GCIB etching apparatus as defined in claim 15 wherein said electrostatic mirror further comprises means for permitting said unwanted ionizing radiation to pass therethrough.
 17. A GCIB etching apparatus as defined in claim 16 wherein said reflective element assembly further comprises a power supply.
 18. A GCIB etching apparatus as defined in claim 1 further comprising means for providing excess electrons to a surface of the substrate.
 19. A GCIB etching apparatus as defined in claim 1 further comprising means for minimizing effects of surface charging on said substrate.
 20. A GCIB etching apparatus as defined in claim 19 wherein said means for minimizing effects of surface charging on said substrate comprises a Faraday enclosure at least partially surrounding the substrate.
 21. A GCIB etching apparatus as defined in claim 1 wherein the substrate contains a fluoropolymer component.
 22. A gas cluster ion beam (GCIB) etching apparatus comprising: a system for producing a gas cluster ion beam utilized to controllably etch a substrate, said gas cluster ion beam initially being directed along a first axis; a portion of the GCIB etching apparatus being operably connected to said beam producing system, said portion containing the substrate to be etched when the substrate is impacted by said gas cluster ion beam; said portion of the GCIB etching apparatus including means for directing said gas cluster ion beam along a second axis in a direction offset from said first axis while permitting unwanted ionizing radiation to remain directed along said first axis; and means within said portion of the GCIB etching apparatus for positioning the substrate in line with said offset gas cluster ion beam; wherein said unwanted ionizing radiation is substantially prevented from impinging upon the substrate during the etching process.
 23. A GCIB etching apparatus as defined in claim 22 wherein said unwanted ionizing radiation contains UV radiation.
 24. A GCIB etching apparatus as defined in claim 22 wherein said unwanted ionizing radiation contains X-ray radiation.
 25. A GCIB etching apparatus as defined in claim 22 wherein said unwanted ionizing radiation contains both UV and X-ray radiation.
 26. A GCIB etching apparatus as defined in claim 22 wherein said unwanted ionizing radiation is electromagnetic radiation.
 27. A GCIB etching apparatus as defined in claim 22 wherein said means for directing said gas cluster ion beam along said second axis comprises means for providing an electrostatic field which deflects said gas cluster ion beam toward the substrate.
 28. A GCIB etching apparatus as defined in claim 27 further comprising a baffle at least partially encompassing the substrate.
 29. A GCIB etching apparatus as defined in claim 28 wherein said baffle includes an entrance portion for permitting said offset gas cluster ion beam to pass onto the substrate.
 30. A GCIB etching apparatus as defined in claim 28 further comprising a collimator in combination with an additional baffle for assisting in the prevention of said unwanted ionizing radiation from reaching the substrate.
 31. A GCIB etching apparatus as defined in claim 29 wherein said baffle comprises material which is capable of absorbing X-ray radiation.
 32. A GCIB etching apparatus as defined in claim 29 wherein said collimator comprises an aperture located within said additional baffle.
 33. A GCIB etching apparatus as defined in claim 22 further comprising a scanning system which is capable of scanning said gas cluster ion beam through a scan angle and wherein said offset gas cluster ion beam is offset at an angle larger than half said scan angle.
 34. A GCIB etching apparatus as defined in claim 22 wherein said offset gas cluster ion beam is offset from said first axis at an angle of approximately 15 degrees.
 35. A GCIB etching apparatus as defined in claim 22 wherein said means for directing said gas cluster ion beam comprises a reflective element assembly which deflects said gas cluster ion beam toward the substrate.
 36. A GCIB etching apparatus as defined in claim 35 wherein said reflective element assembly comprises an electrostatic mirror.
 37. A GCIB etching apparatus as defined in claim 36 wherein said electrostatic mirror further comprises means for permitting said unwanted ionizing radiation to pass therethrough.
 38. A GCIB etching apparatus as defined in claim 35 wherein said reflective element assembly further comprises a power supply.
 39. A GCIB etching apparatus as defined in claim 22 further comprising means for providing excess electrons to a surface of the substrate.
 40. A GCIB etching apparatus as defined in claim 22 further comprising means for minimizing effects of surface charging on said substrate.
 41. A GCIB etching apparatus as defined in claim 40 wherein said means for minimizing effects of surface charging on said substrate comprises a Faraday enclosure at least partially surrounding the substrate.
 42. A GCIB etching apparatus as defined in claim 22 wherein the substrate contains a fluoropolymer component. 